Second state AgxNbS2 occurs in two different modifications, 6RAgxNbS2 and 4HAgxNbS2, both built of sandwiches, NbS2, with the niobium atoms in trigonal-prismatic coordination by sulfur atoms, and with the gaps between sandwiches NbS2 alternately empty and occupied by silver. 6R-AgxNbS2 (0.22 ≦ x ≦ 0.30) of which the structure is known from powder diffraction, a = 3.325 Å, c = 39.59 Å, space group R3m, has silver atoms in trigonally distorted tetrahedra of sulfur atoms. The structure of 4HAg0.22NbS2, prepared by vapour transport, a = 3.334 Å, c = 26.09 Å, space group P63mc, is determined by single crystal X-ray diffraction. In 4HAg0.22 · NbS2 the silver atoms occupy a fraction (0.43) of the octahedral sites between sandwiches NbS2; the silver atoms are ordered two-dimensionally on a √3a × √3a superlattice. A hypothetical phase 4H(c)-NbS2 (known for TaSe2) may be considered to be the host for intercalation. Crystals of both modifications show lattice disorder due to stacking faults. AgxNbS2 zweiter Stufe tritt in zwei verschiedenen Modifikationen auf, 6RAgxNbS2 and 4HAgxNbS2, beide aufgebaut aus Sandwiches NbS2, wobei die Niobatome in der trigonal-prismatischen Koordination durch Schwefelatome ersetzt sind und die Lücken zwischen den NbS2-Sandwiches alternativ leer sind oder mit Silber besetzt. 6RAgxNbS2 (0,22 ≦ x ≦ 0,30), von dem die Struktur aus Pulverbeugung bekannt ist, a = 3,325 Å, c = 39,59 Å Raumgruppe R3m; besitzt Silberatome in trigonal verzerrten Tetraedern von Schwefelatomen. Die Struktur von 4HAg0.22NbS2, das aus der Dampfphase präpariert wird, a = 3,334 Å, c = 26,09 Å. Raumgruppe P63me, wird aus Röntgeneinkristallbeugung bestimmt. In 4HAg0.22NbS2 besetzen die Silberatome einen Teil (0,43) der Oktaederplätze zwischen den NbS2-Sandwiches die Silberatome sind zweidimensional auf einem √3a × √3a-Supergitter angeordnet. Eine hypothetische Phase 4H (c)–NbS2 (bekannt für TaSe2) kann als Wirtsmatrix für Interklation angenommen werden. Kristalle beider Modifikationen zeigen Gitterfehlordnung infolge von Stapelfehlern.
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A single crystal X-ray diffraction study of Ag0.23TaS2 (a = 0.3324 nm, c = 3.948 nm, space group R3m) of a twinned crystal (the observe and the reverse form of the rhombohedron both present) confirms the second stage structure known from powder data. Tantalum atoms are in trigonalprismatic coordination by sulfur atoms (TaS = 0.2475 nm) whereas silver atoms, being located in trigonally distorted tetrahedra of sulfur (AgS = 0.230 nm (1 ×), AgS = 0.265 nm (3 ×)), occupy a fraction of the sites of a honeycomb lattice between sandwiches of TaS2. At 100 K silver atoms are ordered two-dimensionally on a hexagonal 2a × 2a superlattice. Crystals of the stage-2 phase show considerable lattice disorder due to stacking faults. Electron microscopy and diffraction of stage-2 crystals Ag0.39TaS2 grown by vapour transport show that microdomains with hexagonal 2a × 2a ordering are formed below room temperature from a hexagonal a √3 × a √3 superlattice. Complex ordering patterns are observed on cooling. Crystals of composition Ag0.5TaS2 obtained by vapour transport, being intergrowths of stage-1 and stage-2, also show complicated ordering phenomena of the intercalated silver. Mittels Einkristall-Röntgenbeugungsuntersuchung von Ag0.23TaS2 (a = 0,3324 nm, c = 3,948 nm, Raumgruppe R3m) eines verzwillingten Kristalls (der sowohl die Vorderseiten-als auch die Rückseiten-Form des Rhomboeders enthält), kann die aus Pulverdaten bekannte Struktur der zweiten Stufe bestätigt werden. Tantalatome befinden sich in trigonal-prismatischer Koordinierung von Schwefelatomen (TaS = 0,2475 nm), während Silberatome, die in trigonal verzerrten Schwefeltetraeden angeordnet sind (AgS = 0,230 nm (1 ×), AgS = 0,265 nm (3 × )), einen Teil der Plätze eines wabenförmigen Gitters zwischen TaS2-Schichten besetzen. Bei 100 K ist Silber zweidimensional in einem hexagonalen 2a × 2a-übergitter angeordnet. Kristalle der zweiter Stufe zeigen als Folge von Stapelfehlern eine beträchtliche Fehlordnung. Elektronenmikroskopie und -beugung von Ag0.39TaS2-Kristallen der zweiten Stufe, welche über Gasphasentransportreaktion gezüchtet werden, zeigen unterhalb Raumtemperatur die Bildung von Mikrodomänen mit 2a × 2a-überstruktur aus einer hexagonalen √3 a × √3 a-überstruktur. Komplexe Ordnungsmuster werden während des weiteren Abkühlens beobachtet. Durch Gasphasentransport erhaltene Kristalle der Zusammensetzung Ag0.5TaS2 in Form von Verwachsungen der ersten und zweiten Stufe zeigen ebenfalls ein kompliziertes Ordnungsmuster des interkalierten Silbers.
(SnS)1.20TiS2 is a misfit layer compound built of alternately double layers of SnS with distorted rocksalt-type structure and sandwiches of TiS2 slightly distorted compared with those of 1T-TiS2. For comparison with other misfit layer compounds the triclinic subsystems are described in centred unit cells: for the SnS part, a1=5.683(1)AA, b1=5.832(1)AA, c1=11.680(5)AA, alpha 1=95.85(3) degrees , beta 1=94.78(3) degrees , gamma 1=90.03(2) degrees , the space group is C1 and Z=4; for the TiS2 part, a2=3.412(1) AA, b2=5.835(1) AA, c2=23.289(3) AA, alpha 2=95.86(1) degrees , beta 2=90.30(1) degrees , gamma 2=90.01(1) degrees , the space group is F1 and Z=4. In real space, a1 and a2 as well as b1 and b2 are parallel while the c axes diverge. In reciprocal space both sublattices have the (b*,c*) plane in common. Refinements were performed of the SnS part using 1351 independent reflections (RF=0.087) and of the TiS2 part using 714 reflections (RF=0.080). Each Sn atom is coordinated to five S atoms of the SnS double layer with SnS distances of 2.610(3), 2.866(4), 2.873(4), 2.911(4) and 2.976(4) AA, and at larger distances to S of TiS2. The Ti-S distances of the distorted TiS6 octahedra with symmetry 1 are 2.417(2), 2.429(1) and 2.428(1) AA. Sn atoms are between rows of sulphur along a of S of TiS2. The structural relationship with other misfit layer compounds is discussed.
Abstract The ternary title phase with a rhombohedral structure, obtained by reaction between MnTez and Cu at 750°C (3 d) in an evacuated quartz ampoule, is characterized by microprobe analyses, DSC, XRD, resistivity, Hall effect, thermoelectric and magnetic measurements.
